I suppose it all depends on the type of riding/driving you do, and where you do it. There have been instances at work where I have had 4wd engaged and the front diff locked (on the kawi 650), and it still wasn't enough to get me where I wanted to go. On the machine I typically use (honda foreman 450 4x4), I have to keep the 4wd constantly engaged to make it up some of the hills to get close enough to spray the patches of weeds. And even in 4wd, I still don't have enough traction to make it to the top of some of the hills. There have even been instances where I had to get a co-worker to sit on the back rack so that I could back up out of some places. A 2wd machine might get me 1/4 of the way up some of the hills- if I was lucky.

Same goes for 2wd trucks. They just couldn't make it in the mountains here. Sure they can go on dry 2 tracks just fine, but as soon as the snows start hitting, you need 4x4's chained up to travel on many of the roads. I had to dig out a drift in November up elk hunting to get a new Dodge Ram 2500 4x4 chained all the way around past one section of a main BLM road. Later that day, the same Dodge chained all the way around had to hook onto my buddy's 4x4 Suburban with chains on the front and a 24' camper in tow to get us up an icy hill back to the main road.

4 wheel drive is a necesity for most people who drive off road at all times of the year here.